chore: add README.md

README.md

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+# tailcall-valid
+
+This crate helps to collect all possible errors instead of returning the first error encountered. This is useful when you want to know all the errors in a single go.
+
+`Valid` could be initiated with an `Option`, `Result`, success, or a failure.
+
+## Examples
+
+### From success
+
+```rust
+use tailcall_valid::*;
+
+fn main() {
+    let result: Valid<i32, &str> = Valid::succeed(1);
+    assert_eq!(result, Valid::succeed(1));
+}
+```
+
+### From failure
+
+```rust
+use tailcall_valid::*;
+
+fn main() {
+    let err = "Expected a value";
+    let result: Valid<i32, &str> = Valid::fail(err);
+    assert_eq!(result, Valid::from_vec_cause(vec![Cause::new(err)]));
+}
+```
+
+### From `Option`
+
+```rust
+use tailcall_valid::*;
+
+fn main() {
+    // Case when Option is None
+    let err = "Expected a value";
+    let option: Option<i32> = None;
+    let result = Valid::from_option(option, err);
+    assert_eq!(result, Valid::from_vec_cause(vec![Cause::new(err)]));
+
+    // Case when Option is Some
+    let option: Option<i32> = Some(1);
+    let result = Valid::from_option(option, err);
+    assert_eq!(result, Valid::succeed(1));
+}
+```
+
+### From `Result`
+
+```rust
+use tailcall_valid::*;
+
+fn main() {
+    // Case when Result is Err
+    let err = "Expected a value";
+    let result: Result<i32, &str> = Err(err);
+    let result = result.map_err(ValidationError::new);
+    let result = Valid::from(result);
+    assert_eq!(result, Valid::from_vec_cause(vec![Cause::new(err)]));
+
+    // Case when Result is Ok
+    let result: Result<i32, &str> = Ok(1);
+    let result = result.map_err(ValidationError::new);
+    let result = Valid::from(result);
+    assert_eq!(result, Valid::succeed(1));
+}
+```