doc: update keyserver for release keys

sks-keyservers.net is deprecated

Author: tuckbick

README.md

@@ -676,17 +676,17 @@ To import the full set of trusted release keys (including subkeys possibly used
 to sign releases):
 
 ```bash
-gpg --keyserver pool.sks-keyservers.net --recv-keys 4ED778F539E3634C779C87C6D7062848A1AB005C
-gpg --keyserver pool.sks-keyservers.net --recv-keys 94AE36675C464D64BAFA68DD7434390BDBE9B9C5
-gpg --keyserver pool.sks-keyservers.net --recv-keys 74F12602B6F1C4E913FAA37AD3A89613643B6201
-gpg --keyserver pool.sks-keyservers.net --recv-keys 71DCFD284A79C3B38668286BC97EC7A07EDE3FC1
-gpg --keyserver pool.sks-keyservers.net --recv-keys 8FCCA13FEF1D0C2E91008E09770F7A9A5AE15600
-gpg --keyserver pool.sks-keyservers.net --recv-keys C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8
-gpg --keyserver pool.sks-keyservers.net --recv-keys C82FA3AE1CBEDC6BE46B9360C43CEC45C17AB93C
-gpg --keyserver pool.sks-keyservers.net --recv-keys DD8F2338BAE7501E3DD5AC78C273792F7D83545D
-gpg --keyserver pool.sks-keyservers.net --recv-keys A48C2BEE680E841632CD4E44F07496B3EB3C1762
-gpg --keyserver pool.sks-keyservers.net --recv-keys 108F52B48DB57BB0CC439B2997B01419BD92F80A
-gpg --keyserver pool.sks-keyservers.net --recv-keys B9E2F5981AA6E0CD28160D9FF13993A75599653C
+gpg --keyserver pgp.mit.edu --recv-keys 4ED778F539E3634C779C87C6D7062848A1AB005C
+gpg --keyserver pgp.mit.edu --recv-keys 94AE36675C464D64BAFA68DD7434390BDBE9B9C5
+gpg --keyserver pgp.mit.edu --recv-keys 74F12602B6F1C4E913FAA37AD3A89613643B6201
+gpg --keyserver pgp.mit.edu --recv-keys 71DCFD284A79C3B38668286BC97EC7A07EDE3FC1
+gpg --keyserver pgp.mit.edu --recv-keys 8FCCA13FEF1D0C2E91008E09770F7A9A5AE15600
+gpg --keyserver pgp.mit.edu --recv-keys C4F0DFFF4E8C1A8236409D08E73BC641CC11F4C8
+gpg --keyserver pgp.mit.edu --recv-keys C82FA3AE1CBEDC6BE46B9360C43CEC45C17AB93C
+gpg --keyserver pgp.mit.edu --recv-keys DD8F2338BAE7501E3DD5AC78C273792F7D83545D
+gpg --keyserver pgp.mit.edu --recv-keys A48C2BEE680E841632CD4E44F07496B3EB3C1762
+gpg --keyserver pgp.mit.edu --recv-keys 108F52B48DB57BB0CC439B2997B01419BD92F80A
+gpg --keyserver pgp.mit.edu --recv-keys B9E2F5981AA6E0CD28160D9FF13993A75599653C
 ```
 
 See the section above on [Verifying Binaries](#verifying-binaries) for how to